The present invention relates to three dimensional displays.
The term xe2x80x9cautostereoscopicxe2x80x9d as used herein is defined to mean providing parallax information without requiring the use of a viewing aid. The term xe2x80x9cstereoscopicxe2x80x9d as used herein is defined to mean providing parallax information with a viewing aid.
FIG. 1 of the accompanying drawings shows an autostereoscopic display of the type disclosed in EP-A-0 602 934. Light from an illuminator 1 is equally divided by a beam splitter 2, for instance comprising a partially silvered mirror, between transmitted and reflected beams. The transmitted beam is reflected by a mirror 3 via a lens 4 and through a spatial light modulator (SLM) in the form of a liquid crystal display (LCD) panel 5. The reflected beam is similarly reflected by a mirror 6 through a lens 7 and an SLM 8 in the form of an LCD panel. A beam combiner 9, for instance comprising a partially silvered mirror, reflects light from the LCD panel 5 and transmits light from the LCD panel 8. The lenses 4 and 7 form images of the illuminator 1 at respective viewing zones where the eyes of an observer 10 are located. Thus, the left eye of the observer 10 sees an image formed on the LCD panel 8 whereas the right eye sees an image formed on the LCD panel 5. By displaying suitable two dimensional images on the panels 5 and 8 representing views of an object taken from different directions corresponding to the eyes of an observer, the observer 10 sees a three dimensional image which is autostereoscopic i.e. no viewing aids are required.
The display shown in FIG. 1 makes good use of the light provided by the illuminator 1 so as to provide a relatively bright three dimensional image to the observer 10. However, because the autostereoscopic imaging is based on imaging of the illuminator 1 at positions corresponding to the eyes of the observer 10, the autostereoscopic three dimensional image is viewable in a relatively limited region of space so that the observer 10 has a limited freedom of location.
FIG. 2 of the accompanying drawings shows another autostereoscopic three dimensional (3D) display of the type disclosed in EP 0 656 555. The display shown in FIG. 2 is of the same general type as that shown in FIG. 1 in that it uses a beam combiner 9 to combine two dimensional images and effectively a single illuminator whose light is divided by a beam splitter 2. However, the display of FIG. 2 differs from that shown in FIG. 1 in that the fixed relatively small illuminator 1 is replaced by a programmable illuminator 11 which provides or simulates a movable light source. The illuminator 11 is controlled by an observer tracking system 12 which determines the location of an observer and controls the illuminator 11 so that the images of the illuminator are formed at the current locations of the eyes of the observer. As illustrated in FIG. 2, the illuminator 11 comprises a plurality of light emitting areas which are controlled so as to simulate a moving light source. When the observer is at the location indicated at 10a, the portion 11a of the illuminator 11 is illuminated whereas, when the observer is at the position indicated at 10b, the portion 11b of the illuminator 11 is illuminated.
It is thus possible to provide an autostereoscopic display in which the observer can be tracked within a more extended region within which the 3D image is viewable. By tracking more than one observer and controlling the illuminator 11 such that more than one corresponding region is illuminated, it is possible to arrange for the 3D image to be viewable by more than one observer. However, the viewing region may still be undesirably limited and only a limited number of observers can be accommodated. Further, the complexity and cost of the display are increased by the provision of the observer tracking system 12.
U.S. Pat. No. 5,264,964 discloses an imaging system which is capable of operating in both stereoscopic and autostereoscopic modes, which are illustrated in FIGS. 3 and 4, respectively, of the accompanying drawings. A spatially multiplexed stereoscopic image formed of alternating left eye view strips L and right eye view strips R is disposed below micropolarising arrays PA1, PA2 and PA3. Polarisers having a first linear polarisation direction are denoted by P1 whereas polarisers having a second linear polarisation direction orthogonal to the first linear polarisation direction are denoted by P2. Transparent non-polarising regions are denoted by T. Polarisers P1 of the array PA1 are disposed on the strips L whereas polarisers P2 of the array PA1 are disposed on the strips R.
The arrays PA2 and PA3 are spaced from the array PA1 and each comprises a repeating pattern of regions P1, P, P2. In the stereoscopic mode illustrated in FIG. 3, regions of the same type of the arrays PA2 and PA3 are aligned with each other. In the autostereoscopic mode illustrated in FIG. 4, polarising regions of different types of the arrays PA2 and PA3 are aligned with each other to provide opaque regions which alternate with the transparent regions T to form a parallax barrier.
The arrays PA2 and PA3 are moved relative to each other to change between the stereoscopic and autostereoscopic modes.
As shown in FIG. 3; light is transmitted in regions A from the strips R via the transparent regions T to the right eye of an observer. In regions B, light is transmitted from the strips R via regions P2 of the arrays PA2 and PA3 to the right eye. Because of differences in transmissivity between the regions T and P2, the image portions viewed via the regions B will be darker than the image portions viewed via the regions A. In region C, light from the strip R2 towards the right eye is absorbed by the orthogonal polarisers P1 and P2 so that a dark band with be visible in the image. In regions D, light from the strips L towards the right eye is absorbed by the orthogonal polarisers so that the left eye view strips are not visible to the right eye.
Light from the strip R1 is mostly transmitted to the right eye whereas light from the strip R2 is mostly blocked from the right eye. Similar effects occur for the left eye of the observer. Thus, different parts of the same view have different intensities when seen by the observer. Further, the pars of the views at least partially obscured by orthogonal polarisers change for different positions of the observer so that intensity fluctuations are seen across the display as the observer moves.
In the autostereoscopic mode illustrated in FIG. 4, there is a problem with the size of the slit width of the parallax barrier. For a slit width equal to the barrier width and for a typical position of the observer as shown, the right eye sees a right eye view strip R3 via a region E but also sees part of a left eye view strip L1 via a region F. The left eye sees only part of the strip L1 via a region G but sees the right eye view strip R4 via a region H. A substantial amount of cross-talk is therefore visible in the image.
The amount of cross-talk varies with the angle between the display and the eyes of the observer so that, for each position of the observer, different parts of the display exhibit different levels of cross-talk. Also, as the observer moves, the amount of cross-talk seen by each eye varies.
In order to reduce the cross-talk, the slit width may be made narrow. However, this results in a deterioration of image quality in the stereoscopic mode. Thus, for the display to operate in both the autostereoscopic and stereoscopic modes, conflicting demands on the slit width result in poor image quality in both modes or in the image quality in one mode being sacrificed for the image quality in the other mode.
A further disadvantage with the system disclosed in U.S. Pat. No. 5,264,964 is the tight alignment tolerances required of the micropolariser arrays. Substantial cost and difficulty of manufacture are necessary in order to provide the required tolerances.
According to a first aspect of the invention, there is provided a display as defined in the appended claim 1.
According to a second aspect of the invention, there is provided a display as defined in the appended claim 23.
Preferred embodiments of the invention are defined in the other appended claims.
It is thus possible to provide a 3D display which can be operated in an autostereoscopic mode, which does not require any viewing aids, or in a stereoscopic mode, which does require viewing aids such as suitable polarised spectacles to be worn by an observer. In the autostereoscopic mode, a relatively bright image can be provided but is viewable in only a relatively limited viewing region. In the stereoscopic mode, although the image may be less bright for the same illumination power, the 3D image is viewable over a substantially extended region. This provides a much larger freedom of observer location and allows more than one observer to view the display without the requirement for observer tracking. Good image quality is provided in both modes and no extraordinary manufacturing tolerances are required.
It is also possible to provide an autostereoscopic display exhibiting reduced cross-talk between left and right images.
Displays of this type may be used, for instance, in 3D television, 3D computer aided design and graphics, 3D medical imaging, virtual reality, and computer games.